\mode<presentation>

\definecolor{essblue}{rgb}{0.0, 0.655, 0.816}
\definecolor{essgrey}{rgb}{0.537, 0.537, 0.537}

\setbeamercolor*{title page header}{fg=white}
\setbeamercolor*{subtitle}{fg=essgrey}
\setbeamercolor*{author}{fg=white}
\setbeamercolor*{date}{fg=white}

\setbeamercolor*{item}{fg=essblue}

\mode<all>